The present invention relates to a composition comprising an aqueous solution of an acid suppressible rheology modifier, more particularly, a hydrophobically modified alkylene oxide polymer, and a phosphoric acid ester surfactant. The composition of the present invention exhibits improved stability against phase separation.
Rheology modifiers (also known as thickeners) are advantageously combined with aqueous dispersions of film-forming polymer particles (binder) to obtain the desired degree of viscosity in coatings formulations. Thickeners of particular interest are hydrophobically modified alkylene oxide polymers, more particularly hydrophobically modified ethylene oxide urethane polymers (HEURs), which enjoy widespread commercial use.
In recent years, Bobsein et al. (U.S. Pat. No. 7,741,402 B2) described an approach for the efficient preparation of pourable HEURs with concomitant high thickener solids content, by incorporating secondary or tertiary amine or phosphine functionality into the hydrophobic portion of the HEUR, thereby causing thickener suppression under acid conditions and increased thickening efficiency at pH greater than 8. One of the drawbacks of HEURs, however, continues to be their propensity to phase separate, which is believed to result from the presence of water-insoluble small molecule byproducts formed in the preparation of the thickener. This phase separation is unsightly at best and, in extreme cases, causes a reduction in thickening efficiency. It would therefore be an advance in the art to prepare pourable HEURs with high thickener solids without attendant phase separation, while preserving the integrity of the coatings formulation.